The rapid progress of genetic engineering has enabled development of various molecular biological techniques. With the development, remarkable advancements have been shown in analyses of genetic information and functions, and a number of attempts to apply the results to actual therapy have been made. Above all, gene therapy is mentioned as one of the fields which received the greatest development. Various genes relating hereditary diseases have been discovered and decoded, while methods for introducing these genes into cells through physical and chemical techniques have been developed. Thus, gene therapy has now stepped up from the stage of fundamental experiments to actual clinical application.
As it has been clarified that the abnormal gene participates in congenital diseases, such as familial hypercholesterolemia and adenosine deaminase (ADA) deficiency, and cancers and AIDS which are considered as acquired hereditary diseases, gene therapy by transducing the gene to the somatic cells of a patient has been attracting attention as a new method of therapy. After the first clinical test of gene therapy in the United States in 1989, clinical tests were commenced also in Italy, The Netherlands, France, England, and China. In the U.S., in particular, 81 protocols for gene therapy were approved by Recombinant DNA Advisory Committee (RAC) of National Institute of Health (NIH), and about 500 cases underwent gene therapy by June, 1995.
By the kind of the cells to which genes are transduced (target cells), gene therapy is divided into germ cell gene therapy and somatic cell gene therapy. It is also divided into augmentation gene therapy (a new (normal) gene is added with an abnormal gene as it is) and replacement gene therapy (an abnormal gene is replaced with a new (normal) gene). For the time being, only augmentation gene therapy to somatic cells are allowed due to bioethical and technical limitations.
A great technical subject in the above-mentioned clinical application of gene therapy is how to introduce foreign genes into target cells efficiently and safely. Early in 1980, application of physical techniques such as microinjection was attempted but not turned to practical use because the efficiency and stability of gene transduction were low and also because the technique of large scale cell culture was limited in those days. Thereafter, recombinant viruses (virus vectors) serving as a vector for efficient transduction of an foreign gene into target cells were developed, which enabled clinical application of gene therapy for the first time.
One of the most general methods of gene therapy is ex vivo gene therapy by autograft, in which target cells are taken from a patient and, after transducing thereto a gene for therapy, the cells are returned to the patient (see Science, Vol. 249, p. 1285 (1990)). Application of ex vivo gene therapy is limited to those cases in which the cells subject to the therapy can be taken outside the body. In addition, since special equipment is required for mass culture of the cells taken from the patient, the facilities available for the therapy are limited.
On the other hand, for the cases where the target cells are fixed at an organ or tissues, so-called in vivo gene therapy has been studied, in which a gene for treatment is administered directly to the site from which the disease is originated. For example, a method for transducing a gene into an organ, such as the heart or the liver, comprising inserting a balloon catheter through a blood vessel and, after stopping the blood flow, directly infusing the gene to the inner wall of the blood vessel has been proposed (see unexamined published Japanese patent application 6-509328 based on a PCT application PCT/US92/05242 (International Publication No. WO93/00051)).
Clinical researches of in vivo gene therapy for cerebroma (see Human Gene Therapy, Vol. 4, p. 39 (1993)) or malignant melanoma (Blood, Vol. 80, p. 2817 (1992)) have also been carried on. Such in vivo gene therapy is expected as a new method taking the place of conventional surgical treatment or chemotherapy.
Gene therapy for cancers is generally divided into indirect killing of cancer cells and direct killing of cancer cells.
The former is a method for treating a cancer by making use of immunity essentially possessed by a living body. More specifically, this method is to make a tumor disappear by enhancing the anti-tumor immunity of the patient by transducing of a gene which codes cytokines, such as interleukin (IL) 2 (see Cell, Vol. 60, p. 397 (1990)), IL 4 (see Cell, Vol. 57, p. 503 (1989)), interferon (INF) .gamma. (see Proc. Natl. Acd. Sci. U.S.A., Vol. 86, p. 9456 (1989)), a granulocyte-macrophage colony-stimulating factor (GM-CSF) (see Proc. Natl. Acd. Sci. U.S.A., Vol. 90, p. 3539 (1993)), and a tumor necrosis factor (TNF) (see J. Immunolo., Vol. 146, p. 3227 (1991)), and an intercellular adhesive factor (see Science, Vol. 259, p. 368 (1993)). With respect to the mechanism of the tumor disappearance, induction of cytotoxic T lymphocytes (CTL) and tumor infiltrating lymphocytes (TIL) has been reported (see Science, Vol. 256, p. 808 (1992)).
The latter therapy is a method of introducing a gene directly acting on cancer cells. Specifically, this method is characterized in that a gene coding an enzyme capable of converting a cytotoxin precursor to an activated form is transduced into cancer cells, and the cytotoxin precursor is administered locally or systemically thereby to specifically kill the transduced cancer cells. The method is called virus-directed enzyme/prodrug therapy (VDEPT). For example, introduction of a self-killing gene, such as a thymidine kinase (tk) gene of herpes simplex virus (HSV), combined with ganciclovir (GCV) is mentioned (see Science, Vol. 256, p. 1550 (1992)). The cells to which the tk gene has been transduced metabolize GCV to produce cytotoxic GCV-triphosphate (GCV-TP) and thereby suffer injury and death. At this time, a lethal effect occurs also in the cancer cells into which the gene has not been integrated (a so-called bystander effect) and the tumor reduces (see Human Gene Therapy, Vol. 4, 725 (1993)). Further, in cases where carcinogenesis is induced by variation of anti-oncogene, such as p53 and Rb, transduction of the anti-oncogene has been suggested in an attempt to normalize the cells (see Science, Vol. 249, p. 912 (1990)).
About a half of cases of gastric cancer, one of digestive organ cancers, are now found in the initial stage owing to the recent highly advanced medical techniques, and more than a half of the cases can be cured completely. However, advanced cases of gastric cancer are still incurable even with every possible treatment, and establishment of new therapy has been keenly demanded.
The conventional treatment for gastric cancer is generally divided into (1) surgical treatment and (2) chemotherapy as described below.
(1) Standard surgical therapy generally applied to gastric cancer is the extended radical surgery comprising complete extirpation of not only the stomach inclusive of the lesion but the surrounding lymph nodes. However, the recent rapid advancement of medical treatment on gastric cancer has allowed application of reduced surgery comprising removal of the affected site to cases with gastric cancer at the early stage with little possibility of spread to lymph nodes. The reduced surgery includes endoscopic mucosal resection, laparoscopic local resection of the stomach, and the like, and the scale of the operation is decided according to the depth of the affected part. PA0 (2) For the gastric cancer that cannot be completely resected or with observed metastasis to lymph nodes, endoscopic chemotherapy is adopted for the purpose of extirpation of the affected lymph nodes. This method is medication for complete extirpation chiefly aiming at metastatic lesions in lymph nodes that are difficult to extirpate by surgical means. Drugs comprising a lymph-directed carrier, such as an emulsion, liposomes, or fine activated carbon powder, having included therein or adsorbed thereon an anticancer agent are used for the chemotherapy. The anticancer agents include 5-FU, adriamycin, mitomycin C, and so on. However, there is a possibility of occurrence of side effects, such as epilation, reduction of leucocytes, and internal organ disturbances. While it has been proposed to previously transduce a multidrug-resistant gene (MDR-1) into hematopoietic stem cells to endow the patient with resistant against chemotherapy, chemotherapy serves as nothing but preoperative auxiliary treatment for the time being.
Endoscopic mucosal resection (see Takemoto, T. et al., Digest Endosco., Vol. 1, No. 1, p. 4 (1989)) is a surgical treatment involving no laparotomy. Strip biopsy is widely performed as one embodiment of endoscopic mucosal resection, in which the lesion is lifted by submucous infusion of physiological saline and resected by means of a direct vision 2-channel scope. Strip biopsy is advantageous in that the time for an operation and anesthesia can be reduced and the amount of transfused blood is smaller than that needed in a standard surgical operation so that hepatic disorders can be minimized and the pain or burden on a patient can be alleviated. Although complete extirpation of the surrounding lymph nodes is difficult because the resectable area is limited, an increased capacity of the remaining stomach is secured, making it possible to improve the patient's postoperative quality of life (QOL). However, the cases to which strip biopsy is applicable are limited to those with protuberant tumors having a diameter of smaller than 2 cm and depressed tumors having a diameter of smaller than 1 cm.
For the management of larger lesions which should be removed by divided endoscopic mucosal resection and raise a possibility of increasing an incomplete resection ratio, laparoscopic local stomach resection (see Ohgami, M. et al., Dig. Surg., Vol. 11, pp. 64-67 (1994)) is effective. However, the gas in the stomach may escape through the possible perforation made for the resection. It may follow that the visual field is lost due to deflation of the stomach, which sometimes forces switch-over to laparotomy.
The above-mentioned reduced surgery gives rise to problems of occurrence of multiple cancer and carcinogenesis of the residual stomach and also involves a possibility of metastases. Therefore, care should be taken in resection not to bring the tumor tissue into contact with other tissues. Further, the target of the reduced surgery is a primary cancer that can be surgically resected with ease and accordingly is not expected to have effects on metastatic lesions in lymph nodes.
Anyway, the above-mentioned therapeutic methods differ in applicability, and there has not been established therapy aiming at a tumor site and surrounding lymph nodes at the same time.